1. Field of the Invention
The present invention relates to an elastic wave device including an area on a piezoelectric substrate where a plurality of wires have a bridged structure, and to a method for manufacturing such a device.
2. Description of the Related Art
Elastic wave devices have thus far been widely used as duplexers in cellular phones and the like. With this type of elastic wave device, a very large number of wires are routed on the piezoelectric substrate. Accordingly, a structure in which, on a piezoelectric substrate, wires bridge each other with an inorganic insulating film provided therebetween is known, as disclosed in Japanese Patent No. 5141852. According to Japanese Patent No. 5141852, interdigital transducer electrodes and wires having bridged areas are formed on the piezoelectric substrate. A support member and a cover material made from a resin are also laminated onto the piezoelectric substrate, forming a hollow area.
Meanwhile, according to International Publication No. WO 2009/116222, interdigital transducer electrodes and wires having bridged areas are provided on a piezoelectric substrate. The bridged areas are exposed from an opening provided in a support member made from a resin such that the bridged areas are not covered by the support member.
Japanese Unexamined Patent Application Publication No. 2009-182407, discloses bridged areas of wires having an interlayer insulating film made from a resin being provided on a substrate.
According to the elastic wave device disclosed in Japanese Patent No. 5141852, there is a risk that at the bridged areas, cracks or wire breakage will arise in the wires on the inorganic insulating film due to non-planarities in the inorganic insulating film or non-planarities produced by wires in lower areas. There is a further problem in that differences in the coefficient of linear expansion between the support member made from a resin and the piezoelectric substrate make it easy for a large amount of thermal stress to arise in the wires on the inorganic insulating film.
On the other hand, in International Publication No. WO 2009/116222, the bridged areas are not covered by the support member made from a resin. Accordingly, thermal stress can be alleviated. However, this reduces the freedom of design and makes it difficult to make the device smaller. There has also ultimately been a risk of cracks or elasticity problems arising in the wires on the inorganic insulating film.
The interlayer insulating film is made from a resin in the bridged areas according to Japanese Unexamined Patent Application Publication No. 2009-182407. The surface of the interlayer insulating film is rounded as a result. This makes it difficult for cracks, wire breakage, and so on to form in wires in upper areas.
However, with an interlayer insulating film made from a resin, there is still a large difference in the coefficient of linear expansion between the piezoelectric substrate and the resin, and thus there is a problem that a large amount of thermal stress arises in the wires on the insulating layer.